asm-generic: partially revert "Unify uapi bitsperlong.h for arm64, riscv and loongarch"

Unifying the asm-generic headers across 32-bit and 64-bit architectures
based on the compiler provided macros

asm-generic: partially revert "Unify uapi bitsperlong.h for arm64, riscv and loongarch"

Unifying the asm-generic headers across 32-bit and 64-bit architectures
based on the compiler provided macros was a good idea and appears to work
with all user space, but it caused a regression when building old kernels
on systems that have the new headers installed in /usr/include, as this
combination trips an inconsistency in the kernel's own tools/include
headers that are a mix of userspace and kernel-internal headers.

This affects kernel builds on arm64, riscv64 and loongarch64 systems that
might end up using the "#define __BITS_PER_LONG 32" default from the old
tools headers. Backporting the commit into stable kernels would address
this, but it would still break building kernels without that backport,
and waste time for developers trying to understand the problem.

arm64 build machines are rather common, and on riscv64 this can also
happen in practice, but loongarch64 is probably new enough to not
be used much for building old kernels, so only revert the bits
for arm64 and riscv.

Link: https://lore.kernel.org/all/[email protected]/
Reported-by: Nathan Chancellor <[email protected]>
Fixes: 8386f58f8deda ("asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch")
Acked-by: Catalin Marinas <[email protected]>
Acked-by: Palmer Dabbelt <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

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asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch

Now we specify the minimal version of GCC as 5.1 and Clang/LLVM as 11.0.0
in Documentation/process/changes.rst, __CHAR_BIT__ and

asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch

Now we specify the minimal version of GCC as 5.1 and Clang/LLVM as 11.0.0
in Documentation/process/changes.rst, __CHAR_BIT__ and __SIZEOF_LONG__ are
usable, it is probably fine to unify the definition of __BITS_PER_LONG as
(__CHAR_BIT__ * __SIZEOF_LONG__) in asm-generic uapi bitsperlong.h.

In order to keep safe and avoid regression, only unify uapi bitsperlong.h
for some archs such as arm64, riscv and loongarch which are using newer
toolchains that have the definitions of __CHAR_BIT__ and __SIZEOF_LONG__.

Suggested-by: Xi Ruoyao <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Suggested-by: Arnd Bergmann <[email protected]>
Link: https://lore.kernel.org/linux-arch/[email protected]/
Signed-off-by: Tiezhu Yang <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

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